TheSwiftBAT X‐Ray Survey. III. X‐Ray Spectra and Statistical Properties

M. Ajello, A. Rau, J. Greiner, G. Kanbach, M. Salvato, A. W. Strong, S. D. Barthelmy, N. Gehrels, C. B. Markwardt, J. Tueller
2008 Astrophysical Journal  
In this concluding part of the series of three papers dedicated to the Swift/BAT hard X-ray survey (BXS), we focus on the X-ray spectral analysis and statistical properties of the source sample. Using a dedicated method to extract time-averaged spectra of BAT sources we show that Galactic sources have, generally, softer spectra than extragalactic objects and that Seyfert 2 galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert galaxies is consistent with a power-law with
more » ... power-law with photon index of 2.00 (+/-0.07). The cumulative flux-number relation for the extragalactic sources in the 14-170 keV band is best described by a power-law with a slope alpha=1.55 (+/-0.20) and a normalization of 9.6±1.9 × 10^-3 AGN deg^-2 (or 396(+/-80) AGN all-sky) above a flux level of 2× 10^-11erg cm^-2 s^-1 ( 0.85 mCrab). The integration of the cumulative flux per unit area indicates that BAT resolves 1-2 sub-sample of 24 extragalactic sources above the 4.5 sigma detection limit is used to study the statistical properties of AGN. This sample comprises local Seyfert galaxies (z=0.026, median value) and 10 the Seyfert galaxies are absorbed by column densities of Log(N_H)>22, but that none is a bona fide Compton-thick. This study shows the capabilities of BAT to probe the hard X-ray sky to the mCrab level.
doi:10.1086/524104 fatcat:m3pya37wcvduha2plcyrvpbsaa